/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.flink.table.runtime.operators.window.assigners;

import org.apache.flink.api.common.ExecutionConfig;
import org.apache.flink.api.common.typeutils.TypeSerializer;
import org.apache.flink.table.dataformat.BaseRow;
import org.apache.flink.table.runtime.operators.window.TimeWindow;

import java.time.Duration;
import java.util.Collection;
import java.util.Collections;

/**
 * A {@link WindowAssigner} that windows elements into fixed-size windows
 * based on the timestamp of the elements. Windows cannot overlap.
 */
public class TumblingWindowAssigner extends WindowAssigner<TimeWindow> implements InternalTimeWindowAssigner {

	private static final long serialVersionUID = -1671849072115929859L;
	/**
	 * Size of this window.
	 */
	private final long size;

	/**
	 * Offset of this window.  Windows start at time
	 * N * size + offset, where 0 is the epoch.
	 */
	private final long offset;

	private final boolean isEventTime;

	protected TumblingWindowAssigner(long size, long offset, boolean isEventTime) {
		if (size <= 0) {
			throw new IllegalArgumentException
				("TumblingWindowAssigner parameters must satisfy size > 0");
		}
		this.size = size;
		this.offset = offset;
		this.isEventTime = isEventTime;
	}

	@Override
	public Collection<TimeWindow> assignWindows(BaseRow element, long timestamp) {
		long start = TimeWindow.getWindowStartWithOffset(timestamp, offset, size);
		return Collections.singletonList(new TimeWindow(start, start + size));
	}

	@Override
	public TypeSerializer<TimeWindow> getWindowSerializer(ExecutionConfig executionConfig) {
		return new TimeWindow.Serializer();
	}

	@Override
	public boolean isEventTime() {
		return isEventTime;
	}

	@Override
	public String toString() {
		return "TumblingWindow(" + size + ")";
	}

	// ------------------------------------------------------------------------
	//  Utilities
	// ------------------------------------------------------------------------

	/**
	 * Creates a new {@code TumblingWindowAssigner} {@link WindowAssigner} that assigns
	 * elements to time windows based on the element timestamp.
	 *
	 * @param size The size of the generated windows.
	 * @return The time policy.
	 */
	public static TumblingWindowAssigner of(Duration size) {
		return new TumblingWindowAssigner(size.toMillis(), 0, true);
	}

	/**
	 * Creates a new {@code TumblingWindowAssigner} {@link WindowAssigner} that assigns
	 * elements to time windows based on the element timestamp and offset.
	 *
	 * <p>For example, if you want window a stream by hour,but window begins at the 15th minutes
	 * of each hour, you can use {@code of(Time.hours(1),Time.minutes(15))},then you will get
	 * time windows start at 0:15:00,1:15:00,2:15:00,etc.
	 *
	 * <p>Rather than that,if you are living in somewhere which is not using UTC±00:00 time,
	 * such as China which is using UTC+08:00,and you want a time window with size of one day,
	 * and window begins at every 00:00:00 of local time,you may use {@code of(Time.days(1),Time.hours(-8))}.
	 * The parameter of offset is {@code Time.hours(-8))} since UTC+08:00 is 8 hours earlier than UTC time.
	 *
	 * @param offset The offset which window start would be shifted by.
	 * @return The time policy.
	 */
	public TumblingWindowAssigner withOffset(Duration offset) {
		return new TumblingWindowAssigner(size, offset.toMillis(), isEventTime);
	}

	public TumblingWindowAssigner withEventTime() {
		return new TumblingWindowAssigner(size, offset, true);
	}

	public TumblingWindowAssigner withProcessingTime() {
		return new TumblingWindowAssigner(size, offset, false);
	}
}
